The present invention relates to an apparatus and method for forming logs of sheet material in the winding cradle of a rewinder. More particularly, the present invention relates to an apparatus and method for forming logs of sheet material having a desired diameter.
In the production of consumer roll goods such as bathroom tissue, paper towels, wipers, or other sheet material, rewinders are used to convert large diameter parent rolls of sheet material into numerous small diameter, narrow width rolls for consumer use. During the rewinding process, the sheet material on the large diameter parent roll is unwound, then rewound into smaller diameter logs. Optional converting steps may include slitting, embossing, and/or perforating.
Rewinders may be continuous or non-continuous. After the formation of a log in a non-continuous rewinder, the rewinder is stopped, the log is ejected, a new set of cores is inserted in the winding cradle, and the rewinder is started again for another cycle. Economics dictate that this cycle time must be as short as possible. In a continuous rewinder, the rewinder may be slowed, but does not come to a complete stop during the ejection of a log.
After a log reaches the target diameter, the log is ejected from the winding cradle so that it may be advanced to a series of further processing steps, for example a packaging step. However, in some instances the log may not reach the target diameter, for example, if the sheet material were to break prior to reaching the target diameter. In this case, the log is still ejected from the winding cradle, but is advanced to a different series of further processing steps, for example a reclaiming step. Therefore, separation of the defective logs from those that achieve the target diameter is needed to help ensure product uniformity.
Mechanical devices such as pushers may be used to eject the finished log from the rewinder. However, mechanical pushers may have a slow cycle time and may require a rather large minimum log diameter before the pusher can be activated to reject the log from the rewinder. If the sheet material web breaks prior to reaching the minimum log diameter, the rewinder operator is often required to re-thread the broken web and build the log to the minimum log diameter before it can be rejected from the rewinder. This can create an enormous amount of wasted time and/or sheet material.
Therefore, there exists a need for an improved rewinder apparatus and an improved method of removing logs from a surface-driven rewinder. In this regard, there exists a need for a rewinder and method that decreases the amount of time that is required to eject a completed log from a surface-driven rewinder. There further exists a need for a rewinder and method that eliminates the need to build a defective log to a minimum diameter prior to rejecting the defective log from a surface-driven rewinder. Still further, there exists a need for a rewinder and method for separating logs of target diameter from defective logs.
The aforesaid needs are fulfilled and the problems experienced by those skilled in the art overcome by the rewinder of the present invention which, in one aspect, comprises a winding cradle formed by a plurality of parallel rollers wherein at least one of the rollers is moveable relative to the others thereby forming at least two gaps of variable length. The rewinder further comprises a first driver that is operatively connected to and controls the speed of at least one of the rollers; and a second driver that is operatively connected to and controls the speed of at least one of the rollers, wherein the rollers driven by the first driver are different than the rollers driven by the second driver. Further, at least one of the rollers is an ejection roller whereby a log or roll of sheet material formed within the winding cradle can be ejected therefrom to either side of the ejection roller.
In a further aspect, a rewinder for forming logs or rolls of sheet material is provided comprising a winding cradle formed by a plurality of parallel rollers having gaps there between and wherein at least one of the rollers is moveable relative to the others thereby forming first and second gaps of variable length; a first driver that is operatively connected to and controls the rotational speed of at least one of the rollers; a second driver that is operatively connected to and controls the rotational speed of at least one of the rollers and wherein the rollers driven by the first driver are different than the rollers driven by the second driver. This rewinder allows a log or roll of sheet material formed within the winding cradle to be ejected through either the first or second gap.
The first and second drivers may, in one aspect, comprise variable speed drivers. Additionally and/or alternatively, the direction of rotation of at least one of the rollers may be capable of being reversed to eject a log from the winding cradle.
In a particular aspect, the plurality of rollers may comprise first, second and third rollers wherein the first and second gaps adjacent the first roller are of variable length. The first driver may be operatively connected to and control the rotational speed of the first roller and the first driver may be a variable speed driver. The first roller may, in one aspect, be moveable relative to the second and third rollers thereby forming the first and second gaps of variable length. The second gap may have a length between 50% and 200% of the length of the first gap. In a further aspect, the first driver may be operatively connected to and control the rotational speed of the first roller and the first driver may be capable of rotating the first roller in clockwise and counter-clockwise directions.
The rewinder may further include a sheet feeding mechanism and a log starting mechanism wherein the sheet feeding mechanism directs the sheet material into the winding cradle. In one aspect, the sheet material may comprise a paper product. In a further aspect, the rewinder may further comprise at least one roller having an anti-slip surface.
In a further aspect of the present invention, a method of forming a log or roll of sheet material is provided comprising the steps of: (i) directing a sheet material into a winding cradle and forming a log or roll of sheet material, wherein the winding cradle is formed by a plurality of rollers having gaps there between and further wherein at least one of the rollers is moveable relative to the others thereby forming first and second gaps of variable length; (ii) rotating the rollers and the log or roll of sheet material thereby increasing the diameter of the log or roll of sheet material in the winding cradle and wherein the first and second gap lengths increase with the diameter of the log or roll of sheet material; and (iii) ejecting logs or rolls of sheet material having a selected diameter through the first gap and ejecting logs or rolls having a non-selected diameter through the second gap.
In a particular aspect of the present invention, the step of ejecting the log of sheet material may comprise reducing the rotational speed of at least one roller, stopping the rotation of at least one roller, and/or reversing the direction of rotation of at least one roller. In a further aspect, the method may further comprise the step of adjusting the force exerted by at least one of the rollers against the log wherein the roller moves away from the winding cradle to allow the log to eject from the winding cradle.
In a further aspect, the plurality of rollers may comprise a first, second and third rollers wherein the first gap is formed between the first and second roller and the second gap is formed between the first and third roller. Further, the first roller may move away from the second and third rollers as the diameter of the log of sheet material increases. In one aspect, the log of sheet material may be ejected from the winding cradle by altering the rotational speed of the rollers wherein the rotational speed of the first roller exceeds the rotational speed of the second or third rollers. In a further aspect, the log of sheet material may be ejected from the winding cradle by altering the rotational speed of the rollers wherein the rotational speed of the first roller is less than the rotational speed of at least one of the second or third rollers. In still a further aspect of the present invention, logs of sheet material having the selected diameter are ejected through the first gap by altering the rotational speed of the first roller relative to the second or third rollers and logs of sheet material having the non-selected diameter are ejected through the second gap by reversing the direction of one of the rollers relative to the rotational direction used to increase the diameter of the logs of sheet material.